For the first time, cathodoluminescence of CdSexTe1-x (with x = 0-1) films grown by molecular beam epitaxy on (211) Si substrates were systematically studied and compared with photoluminescence. The Se mole fraction was consistently determined by x-ray rocking-curve diffraction, wavelength-dispersive spectroscopy, and Rutherford backscattering. The band gap energy, as determined by both cathodoluminescence and photoluminescence, was found consistent with literature. The band gap energy varied parabolically with composition as predicted by theory. The results suggest cathodoluminescence can be used to conveniently map composition fluctuations such as Se segregation in CdSexTe1-x films, with higher spatial resolution than photoluminescence.